A wide variety of portable electric devices are used in commercial and household applications. Examples include electric power tools such as electric drills and saws, electric lawnmowers and hedge trimmers, trouble lights and vacuum cleaners and rug shampooers. Such portable electric devices often have relatively short electric cords and normally are used in conjunction with an extension cord.
A pervasive problem encountered when using a portable electric device with an extension cord is the tendency of the male plug of the device's electric cord to disconnect from the extension cord's female plug as the device is being used. Disengagement commonly occurs when the operator moves the device in a direction away from the extension cord. If all the slack in the cords is taken up, pulling on the device's cord will often result in disengagement of the connected plugs.
To prevent the disengagement of the device's cord from the extension cord during use, a common practice is to tie the two cords together in a simple loop knot adjacent the cord plugs. The plugs are then connected and form part of the loop. During use, it is likely that the device will be moved in a direction away from the extension cord causing the device's cord to pull against the extension cord. Pulling against the extension cord tightens the knot, i.e., the loop becomes smaller, but the plugs are not disconnected.
While tying two electric cords together prevents disconnection of the plug ends, this is not an altogether satisfactory solution to the disconnection problem. Tying the cords necessarily stresses the tied portions of each cord. As the electric device is moved about during use, the knot tightens and further increases the stress on the tied portions of the respective cords. Repeatedly tying an electric cord in this manner will shorten the cord life. Additionally, the knot may be tightened to a point where it is difficult to disconnect the two plugs after the job is finished. Furthermore, as the knot is tightened, the electric device's extending male plug contacts are torqued within the female plug openings. If the torque is sufficient the plug contacts will bend. The male plug contacts may be ruined or, at a minimum, the contacts will have to be straightened prior using the device again. Finally, the loop forming the knot is prone to snagging on obstacles as the electric device is moved about.
A number of designs have been proposed for preventing disengagement or disconnection of two electrical cord plug ends. Most of the designs involve enclosing the connected plugs in a housing. The housing includes interior protrusions which secure the plugs in their connected position even one of the cords is pulled in a direction away from the other cord.
All of the proposed designs have proven less than satisfactory for number of reasons including high cost, lack of durability, the size being too large given the limited space in an average toolbox, difficulty of use, and ineffectiveness.